assert

Description

assert() will check the given
assertion and take appropriate action if
its result is FALSE.

If the assertion is given as a string it
will be evaluated as PHP code by assert().
The advantages of a string assertion are
less overhead when assertion checking is off and messages
containing the assertion expression when
an assertion fails. This means that if you pass a boolean condition
as assertion this condition will not show up as
parameter to the assertion function which you may have defined with the
assert_options() function, the condition is converted
to a string before calling that handler function, and the boolean FALSE
is converted as the empty string.

Assertions should be used as a debugging feature only. You may
use them for sanity-checks that test for conditions that should
always be TRUE and that indicate some programming errors if not
or to check for the presence of certain features like extension
functions or certain system limits and features.

Assertions should not be used for normal runtime operations like
input parameter checks. As a rule of thumb your code should
always be able to work correctly if assertion checking is not
activated.

The behavior of assert() may be configured by
assert_options() or by .ini-settings described
in that functions manual page.

The assert_options() function and/or
ASSERT_CALLBACK configuration directive allow a
callback function to be set to handle failed assertions.

assert() callbacks are particularly useful for
building automated test suites because they allow you to easily
capture the code passed to the assertion, along with information
on where the assertion was made. While this information can be
captured via other methods, using assertions makes it much faster
and easier!

The callback function should accept three arguments. The first
argument will contain the file the assertion failed in. The
second argument will contain the line the assertion failed on and
the third argument will contain the expression that failed (if
any — literal values such as 1 or "two" will not be passed via
this argument). Users of PHP 5.4.8 and later may also provide a fourth
optional argument, which will contain the
description given to assert(), if
it was set.

Parameters

assertion

The assertion.

description

An optional description that will be included in the failure message if
the assertion fails.

Return Values

FALSE if the assertion is false, TRUE otherwise.

Changelog

Version

Description

5.4.8

The description parameter was added. The
description is also now provided to a callback
function in ASSERT_CALLBACK mode as the fourth
argument.

Examples

Example #1 Handle a failed assertion with a custom handler

<?php// Active assert and make it quietassert_options(ASSERT_ACTIVE, 1);assert_options(ASSERT_WARNING, 0);assert_options(ASSERT_QUIET_EVAL, 1);

See Also

User Contributed Notes 8 notes

There's a nice advantage to giving assert() some code to execute, as a string, rather than a simple true/false value: commenting.

<?php

assert('is_int($int) /* $int parameter must be an int, not just numeric */');

// and my personal favoriteassert('false /* not yet implemented */');

?>

The comment will show up in the output (or in your assertion handler) and doesn't require someone debugging to go through your code trying to figure out why the assertion happened. That's no excuse to not comment your code, of course.

You need to use a block comment (/*...*/) because a line comment (//...) creates an "unexpected $end" parse error in the evaluated code. Bug? Could be.(You can get around it with "false // not yet implemented\n" but that screws up the message)

As noted on Wikipedia - "assertions are primarily a development tool, they are often disabled when a program is released to the public." and "Assertions should be used to document logically impossible situations and discover programming errors— if the 'impossible' occurs, then something fundamental is clearly wrong. This is distinct from error handling: most error conditions are possible, although some may be extremely unlikely to occur in practice. Using assertions as a general-purpose error handling mechanism is usually unwise: assertions do not allow for graceful recovery from errors, and an assertion failure will often halt the program's execution abruptly. Assertions also do not display a user-friendly error message."

This means that the advice given by "gk at proliberty dot com" to force assertions to be enabled, even when they have been disabled manually, goes against best practices of only using them as a development tool.

If you expect your code to be able to work well with other code, then you should not make any assumptions about the current state of assert_options() flags, prior to calling assert(): other code may disable ASSERT_ACTIVE, without you knowing it - this would render assert() useless!

To avoid this, ALWAYS set assert_options() IMMEDIATELY before calling assert(), per the C++ paradigm for assertion usage:

In one C++ source file, you can define and undefine NDEBUG multiple times, each time followed by #include <cassert>, to enable or disable the assert macro multiple times in the same source file.

Here is how I workaround this issue in my PHP code:

<?php
//////////////////////////////////////////////////////////////////////
/// phpxAssertHandler_f
//////////////////////////////////////////////////////////////////////
/**
* @desc Handler which also sets up assert options if not being called as handler
Always fatal when assertion fails
Always make sure assertion is enabled
Cannot depend on other code not using assert or using its own assert handler!
USAGE:
// customize error level of assertion (php assert_options() only allows E_WARNING or nothing at all):
phpxAssertHandler_f(E_USER_NOTICE);
// control assertion active state: not dependent on anything another piece of code might do with ASSERT_ACTIVE
$GLOBALS['MY_ASSERT_ACTIVE']=false;
phpxAssertHandler_f(E_USER_NOTICE,$GLOBALS['MY_ASSERT_ACTIVE']);
// use alternate assertion callback function:
// NOTE: pass null as custom options parameter to use default options
// NOTE: pass no values for assert options parameter array elements to use default options
$GLOBALS['MY_ASSERT_ACTIVE']=false;
$GLOBALS['MY_ASSERT_CALLBACK']='myAssertCallback';
phpxAssertHandler_f(
null,
array(
0=>$GLOBALS['MY_ASSERT_ACTIVE'],
3=>$GLOBALS['MY_ASSERT_CALLBACK'],
)
);